Oxygen Vacancy‐Driven Asymmetrical Charge Distribution on Bi‐O‐Sn Sites in Sn‐Doped Bi ₂ MoO ₆ for Efficient Photocatalytic CO ₂ ‐to‐CH ₄ Conversion

Efficient proton‐coupled electron transfer (PCET) at tailored active sites is beneficial for photocatalytic CO 2 reduction, yet the relationship between catalytic sites and performance remains unclear. Herein, p ‐block Sn is introduced into the Bi 2 MoO 6 lattice (Sn‐BMO) via Bi site substitution to construct a novel oxygen vacancy (Ov)‐Bi‐O‐Sn structure, where high‐valence Sn induces Ov formation by lowering the Bi valence state, thereby creating a charge‐asymmetrical region. This unique configuration promotes PCET: Sn acts as H 2 O oxidation site, enabling proton transfer to proximal Bi site connected to Ov that preferentially traps electrons to convert CO 2 . Furthermore, the electronic structure of Bi is modified to optimize Bi 6 p ‐C 2 p hybridization for formation of the key intermediate *CHO with low energy barrier. Consequently, Sn‐BMO exhibits a remarkable CH 4 evolution rate of 207.3 µmol g −1 h −1 with 95.7% CH 4 selectivity in pure water, achieving a record apparent quantum efficiency of 9.4% at 420 nm. This work provides a novel approach to design charge‐asymmetrical active site in multisite catalysts, elucidating how p ‐block elements influence catalytic performance in CO 2 photoreduction.